This invention is directed to a process for the production of a low-silicon, grain oriented electrical steel, such as sheet and strip, and to the product thereof. More particularly, the steel of this invention is characterized by a Goss texture, a crystalline orientation as defined by Miller indices of (110) [001].
Oriented electrical steels have been used for a number of years in the manufacture of transformers and the like. Such steels are characterized by such magnetic properties as high permeability and low core loss. By this combination it is possible to minimize energy losses in the transformer. Typically such prior art oriented electrical steels were produced from steels containing at least 3.0%, by wt., silicon, and one or more grain growth inhibitors, such as manganese sulfide and aluminum nitride. The processing thereof had to be carefully controlled, and was characterized by one or more high temperature anneals.
While high silicon steels remain as a major product in the field of electrical steels, there have been recent efforts to reduce the amount of silicon needed, yet still produce a grain oriented sheet product suitable as a transformer steel.
U.S. Pat. No. 4,251,296 to Thornburg et al represents one such effort to produce the (110) [001] texture in a low alloy steel. Among other steps, critical features are the control of the sulfur, carbon, manganese, and oxygen contents, and an anneal of at least 1 hour between 750.degree. and the AC.sub.1 temperature prior to the final cold reduction.
In U.S. Pat. No. 3,636,579 to Sakakura et al there is disclosed a process for producing single-oriented electrical steel sheet in a steel containing up to 4%, by wt., silicon. The intermediate anneal, i.e. anneal prior to final cold reduction, is for an extended period, and the temperature is adjusted according to the silicon and carbon contents. Additionally, the annealed steel is quenched at a rate of 2.degree. to 200.degree. C. per sec. to at least 400.degree. C. from the maximum annealing temperature.
Unexpectedly, among several features, by the present invention it was discovered that it was possible to design a processing sequence for the production of electrical steels which included a short time, transcritical anneal prior to the final cold reduction of the steel strip. Such feature, along with others of this invention, shall become apparent from the description which follows.